Currently, the field of injection moulding of plastic material offers numerous technical solutions and systems, widely applied, which have been developed for moulding parts which have a form of a solid of rotation, i.e. exhibit cylindrical and/or conical internal and external surfaces or similar that are extending around and along a central axis of symmetry.
By way of example, FIG. 12 shows a generic piece PZ-100, made of plastic, having justly the shape of a solid of rotation with respect to a central axis X of symmetry, which piece PZ-100 is moulded through a system of injection moulding, of a conventional diaphragm type and indicated generally with 100, that is currently used in the technique.
As can be seen from this FIG. 12, the piece PZ-100 is produced and moulded by injecting the plastic material in the molten state, as shown schematically by an arrow MP, in the cavities of a mould, indicated by 101 and represented schematically with dashed-dotted line, through a conduit or central channel 102, which opens into an injection chamber 103, having the form of a circular disc, which chamber is in turn in communication along its circular periphery with the cavities of the mould 101 which define the shape of the piece PZ-100.
In this way, the plastic material MP is supplied from a central area, corresponding to the channel 102, and is injected and distributed in a regular and uniform form into the cavity of the mould 101 which defines the cylindrical surfaces of the piece PZ-100 to be moulded, i.e. along the entire circular development of such surfaces.
This moulding system 100 is able to ensure a good superficial quality and absence of defects, such as junction lines of the flows of the plastic material, in the cylindrical surfaces which define the shape of solid of rotation of the piece PZ-100.
In fact, as said, the injected plastic material MP accesses to and is distributed in a uniform and circular way along these surfaces, whereby the piece once moulded does not show any signs of confluence and division of the flows of the injected plastic material MP.
However this known moulding system 100 is not exempt from problems, and in particular has the significant drawback that the plastic material MP, which fills the channels for the access to the cavity of the mould 101 and solidifies at the end of the injection phase in the same mould 101, material that constitutes the so-called sprue or feedhead indicated with PZ-100′, remains attached to the body of the piece PZ-100, once it has been moulded.
Therefore, this sprue PZ-100′ must be properly removed at a later stage after the moulding of the piece, with a consequent increase of the time of production of the finished piece or part and thereby also with a corresponding increase of the cost of production.
It is also felt in the technical field of injection moulding of plastic material, even by taking into account of the rapid evolution that interests this technology, the need to further optimize the various steps and operations that make up and in which the injection moulding technology is divided, as in particular the important and critical operation of injecting the plastic material into the mould, as well as the need to reduce the relative costs.